18.6.0 Air pollution12.6.0.1 Acid rain, SOx, burning
sulfur, compound3.48 Acid rain and nitrogen oxides, NOx37.42.1 Composition of the atmosphere
and greenhouse gases3.39.0 Carbon monoxide18.6.0.1 Commonly occurring air pollutants, safe
air and clean air18.6.0.2 Indoor air pollution, formaldehyde pollution37.43.1 Global warming and climate
changeExperiments31.4.44 Cottrell smoke precipitator18.6.3 Danger of vehicle exhausts, tailpipe gases16.7.28 Harmful substances in cigarette
smoke 18.6.2.1 Tests for air pollution from burning
refuse 18.6.3.1 Tests for carbon monoxide with a gas
detector18.1.0 Tests for pH
See: pH (Commercial)18.1.0 pH tests18.1.0.1 Acidity and alkalinity6.1.0 Soil acidity, tests for soil pH18.1.1 Tests for pH with universal indicator18.1.2 Tests for pH of water in the laboratory18.1.3 Tests for pH of rain water18.1.4 Tests for pH of standing water18.2.0 Tests for hardness in water
See: Water Testing (Commercial)18.2.6.1 Tests for electrical conductivity with
a conductivity meter18.2.4 Tests for contamination of groundwater from
refuse deposits18.2.3 Tests for soluble solids in rain water18.2.1 Tests for insoluble solids in rain water18.2.2.3 Tests for sulfates in groundwater18.2.0 Total dissolved solids and suspended solids,
Beer-Lambert law18.7.0 Water pollution
See: Water Testing (Commercial)24.0.0 Water (Chemistry) (Experiments)18.7.0 Bottled water18.2.7 Cations and anions in rain, rivers and sea
water35.23.9 Coal seam gas, SG, and coal
to liquid, CTL, projects18.2.6 Conductivity, TDS and electrical conductivity18.6.6 Colour of water18.6.9 Colorimeter tests, test methods12.12.05 Detergent phosphates18.7.1 Drinking water test media18.7.2 Effect of household detergents on freshwater
organisms10.5.7 Gases dissolved in a water sample18.6.7 Hydrogen ion concentration of water18.2.2.2 Iron in drinking water5.41 Keep water clean (Primary)3.3.5 Mercury's silent toll on the world's
wildlife 4.3.11 Micro-organisms and water
pollution35.23.10 Oil shale and fracking,
(hydraulic fracturing) (Geology) 18.2.5 Salinity18.6.5 Smell of water, hydrogen sulfide18.6.8 Temperature of waterNessler's reagent, Tests for ammonium
radical, free and combined ammonia18.2.2.1 Tests for chlorides in groundwater 18.6.6.1 Tests for colour of water18.2.4 Tests for contamination of groundwater from
refuse deposits 18.6.5.1 Tests for smell of water18.5.1 Tests for environment of river, lake or ocean16 Tests for turbidity18.6.7.1 Tests for hydrogen ion concentration
of water 18.4.0 Tests for ions in a water sample18.6.8.1 Tests for temperature of water18.3.0a Tests for air and dissolved oxygen in water18.5.0 Tests for standing water18.6.4 Water tests18.3.0 Gases dissolved in
a water sample
See: Water Testing (Commercial) 10.5.7 Gases dissolved in a water sample18.3.3 Tests for dissolved oxygen, titration18.3.2 Oxygen content of water, dissolved oxygen,
DO (Winkler method)18.3.0a Tests for air and dissolved oxygen in water18.3.1 Tests for air dissolved in a water sample18.5.0 Tests for standing
water (Environmental chemistry)18.5.2 Test for anions in sewage and tap water18.5.1a Eutrophication of waterways18.5.3 Tests for water samples18.5.1 Tests for environment of river, lake or ocean 19 Total solids18.8.0 Tests for water pollution,
(Environmental chemistry)18.3.0a Tests for air and dissolved oxygen in water18.3.1 Tests for air dissolved in a water sampleNessler's reagent, Tests for ammonium
radical, free and combined ammonia18.5.2 Tests for anions in sewage and tap water18.2.2.1 Tests for chlorides in groundwater 18.6.6.1 Tests for colour of water18.2.4 Tests for contamination of groundwater from
refuse deposits18.2.0 Total dissolved solids and suspended solids,
Beer-Lambert law18.2.6.1 Tests for electrical conductivity with
a conductivity meter18.5.1 Tests for environment of river, lake or ocean18.6.7.1 Tests for hydrogen ion concentration
of water18.2.1 Tests for insoluble solids in rain water 18.4.0 Tests for ions in a water sample18.3.3 Tests for dissolved oxygen, titration18.1.3 Tests for pH of rain water6.1.0 Tests for pH of soil, Soil acidity
18.1.4 Tests for pH of standing water18.1.2 Tests for pH of water in the laboratory18.1.1 Tests for pH with universal indicator18.4.1 Tests for phosphate ions in water 18.6.5.1 Tests for smell of water18.2.3 Tests for soluble solids in rain water18.5.0 Tests for standing water18.2.2.3 Tests for sulfates in groundwater18.6.8.1 Tests for temperature of water6.0 Tests for turbidity18.5.3 Tests for water samples18.6.4 Tests for water18.1.0 pH tests
See: pH (Commercial)See 12.10.7.0: Buffer solutions
| 3.9.0 Solubility and solutions
pH tests use an indicator that changes colour with changes in the concentration
of hydrogen ions, or the acidity of the solution.
The pH value of the ocean changes very little when acids or alkalis are
added or when diluted with water because oceans are buffered
solutions.
However, many rivers and lakes are weakly buffered so their pH may change
rapidly if acids or bases are added.
The oceans, and even some rivers and lakes, contain many different equilibrium
reactions.
For example, when carbon dioxide dissolves in the ocean all the following
reaction can occur to produce about pH 8 that remains
constant because of the "carbonate buffer".
The pH of drinking water normally ranges from 5.5 to 9.0.
At pH levels of less than 7.0, corrosion of water pipes may occur, releasing
metals into the drinking water.
This is undesirable and can cause other concerns if concentrations of such
metals exceed recommended limits.
The reactions below produce both H+ and OH- ions,
but [OH-] > [ H+] so the pH value remains steady
at about pH 8.
Phosphates and silicates have chemical reactions that contribute to buffering
capacity.
CO2 (g) <--> CO2 (aq)
H2O + CO2 (aq) <--> H2CO3
H2CO3 <--> H+ + HCO3-
HCO3- <---> H+ + CO32-
HCO3- <---> CO2 (aq) + OH-
CO32- + H2O <---> HCO3-
+ OH-.18.1.0.1 Acidity and alkalinity
See: pH (Commercial)
Instead of listing all the reactions that contribute to pH of oceans and
rivers, you can call the capacity of chemical species together in
the water to neutralize a strong acid acidity or alkalinity, as measured
in a pH value of hydrogen ion concentration.
pH log10(1 / [H+]).
For many lakes and rivers, if the water has values between pH 5.0 and pH
8.0, the water is often sufficiently buffered so that, if acids,
bases or salts are added, the pH value does not change greatly.
Some salts, e.g. ammonium sulfate, ammonium chloride and aluminium chloride,
and some gases, e.g. carbon dioxide and sulfur
dioxide, will increase the acidity of water.
A low alkalinity river or lake may have sudden pH value changes if acid
or acid industrial waste pollute the water.
A sudden change in pH value, below pH 5.0 or above pH 8.0, kills many
organisms, including fish.
Alkalinity is a measure of the presence of bicarbonate, carbonate or hydroxide
constituents.
Concentrations less than 100 ppm are desirable for domestic water supplies.
The recommended range for drinking water is 30 to 400 ppm.
A minimum level of alkalinity is desirable because it is considered a buffer
that prevents large variations in pH.
Alkalinity is not detrimental to humans.
Moderately alkaline water (less than 350 mg / l) in combination with hardness,
forms a layer of calcium or magnesium carbonate that
tends to inhibit corrosion of metal piping.
Many public water utilities employ this practice to reduce pipe corrosion
and to increase the useful life of the water distribution system.
High alkalinity (above 500 mg / l) is usually associated with high pH values,
hardness and high dissolved solids and has adverse effects
on plumbing systems, especially on hot water systems where excessive scale
reduces the transfer of heat to the water.
Water with low alkalinity, < 75 mg / l), e.g. some surface waters and
rainfall, is subject to changes in pH because of dissolved gasses,
which may be corrosive to metallic fittings.18.1.1 Tests for pH with universal indicator
See: pH (Commercial)
Use Universal Indicator with a constant
technique.
Construct a database of the pH of water at the same places, e.g. along
a river bank, but at different times.
Collect many readings and look for patterns.18.1.2 Tests for pH of water
in the laboratory
See: pH (Commercial)See 3.34.3: Carbon dioxide, Solubility
of acidic oxide carbon dioxide in water, acidity of soda water.
Use Universal Indicator to test the pH of deionized water or demineralized
water, tap water, boiled tap water, tank water, bottled
water, non-gaseous mineral water, gaseous mineral water, soda water, fizzy
lemonade.18.1.3 Tests for pH of rain
water
See: pH (Commercial)
Collect rain water in a clean container.
Use Universal Indicator to test the pH of an isolated rain shower (a "rain
incident") the first rain after a dry period, during continued
periods of rain (a "rain episode") during different wind directions, In
an urban area, in a rural area, in an area near an industrial plant,
e.g. a powerhouse or steel works.
Rain water is in equilibrium with the carbon dioxide in the atmosphere
that forms carbonic acid, a weak acid (ka = 1.75 × 10-5),
the solution under normal atmospheric conditions has pH 5.7.
The average pH of rain is pH 5.0, with range of pH 5.6 to pH 4.5, but
in eastern industrialized North America the average pH of
rain water is reported as pH 4.2.18.1.4 Tests for pH of standing
water
See: pH (Commercial)
1. Use Universal Indicator to test the pH of temporary standing waters,
puddles, tree boles, along rivers, shallow and deep water,
main stream and tributary, lake or sea or ocean, including shallow and
deep water, sewage water before and after treatment, rivers,
where they discharge sewage water, effluent discharged into rivers from
factories and industrial plants.
2. Dip the pH meter into solution.
Stir gently for a few seconds, until the readings stabilize.
Record reading.
Rinse pH detector tip with deionized water.18.2.0 Total dissolved solids
and suspended solids, Beer-Lambert law
See: Colorimeters, (Commercial)
See: Water testing colorimeters, (Commercial)
See: Water water quality, colorimeter, (Commercial)
colourimetric tests based on Beer's Law (Beer-Lambert law) are based on
the observation that the higher the concentration of a
substance in a sample, the darker the colour developed in the test, i.e.
more light is absorbed by the sample.
So the intensity of light (electromagnetic radiation) that passes through
a sample diminishes exponentially with the concentration and
thickness of the sample.
Absorption of light depends on the pathway length and concentration of
the material passed through.
The total dissolved solids test measures the total amount of dissolved
minerals in water.
The solids can be iron, chlorides, sulfates, calcium or other minerals
found on the surface of the earth.
The dissolved minerals can produce an unpleasant taste or appearance and
can contribute to scale deposits on pipe walls.
The following levels of total dissolved solids are expressed in mg / Litre:
Less than 500 Satisfactory,
500 to 1 000 Less than desirable,
1 000 to 1 500 Undesirable,
Over 1 500 Unsatisfactory.
The only effective means of reducing total dissolved solids is by using
reverse osmosis; however, removal is not economical.18.2.1 Tests for insoluble
solids in rain water
See: Water water quality, colorimeter, (Commercial)
Use a previously weighed filter paper kept in a desiccator.
Collect the water in a very clean beaker.
Swirl the water sample to keep the dirt suspended and filter 100 mL into
a measuring cylinder.
Note the volume of the filtrate.
Dry the filter paper in the dissector.
Weigh the filter paper and insoluble particles.18.2.2.1 Tests for chlorides
in groundwater
See: Water water quality, colorimeter, (Commercial)
The chlorides in groundwater can occur naturally or be caused by pollution
from sea water or industrial wastes.
Chloride concentration above 250 mg / Litre can produce a distinct taste
in drinking water.
Where chloride content is known to be low, a noticeable increase in chloride
concentrations may indicate pollution from sewage sources.
The following levels of chlorides are expressed in mg / Litre:
0 to 250 Acceptable,
250 to 500 Less than desirable,
500 to 1 000 Undesirable,
Over 1 000 Unsatisfactory.18.2.2.2 Iron in drinking
water
See: Water water quality, colorimeter, (Commercial)
The iron in drinking water can give a rusty colour to laundered clothes
and may affect taste.
Frequently found in water because of large deposits in the surface of
the earth.
Iron can also be introduced into drinking water from iron pipes in the
water distribution system.
In the presence of hydrogen sulfide, iron causes a sediment to form that
may give the water a blackish colour.
Maximum concentration for iron in drinking water of 1.0 mg /Litre.
The following levels of iron (Fe) are expressed in mg / Litre:
0 to 0.3 Acceptable,
0.3 to 1.0 Satisfactory (however, may cause staining and objectionable
taste)
Over 1.0 Unsatisfactory.
Iron as it exists in natural groundwater is in the soluble (ferrous) state
but, when exposed to oxygen, is converted into the insoluble
(ferric) state with its characteristic reddish brown or rusty colour.
If allowed to stand long enough, this rusty sediment will usually settle
to the bottom of a container.
However, it is difficult to use this type of settling to remove the iron.
The four options for removing iron from potable water are as follows:
1. For dissolved iron in concentrations up to 2.0 mg / litre, add food
grade phosphate that sequesters the dissolved iron, i.e. keeps the
iron in solution.
2. Zeolite softening can remove up to 10 mg / litre of dissolved iron.
3. Potassium permanganate can remove up to 10 mg / litre of iron and will
remove dissolved as well as particulate iron.
The permanganate provides oxygen to oxidize and precipitate any dissolved
iron.
4. Liquid chlorine solution can be used for any quantity of iron, dissolved
or not, and kill iron bacteria.18.2.2.3 Tests for sulfates
in groundwater
See: Water water quality, colorimeter, (Commercial)
The sulfates in groundwater are caused by natural deposits of magnesium
sulfate, calcium sulfate or sodium sulfate.
Concentrations should be below 250 ppm.
Higher concentrations cause laxative effects.
Sulfates cannot be economically removed from drinking water.
The following levels of sulfates are expressed in mg / l:
1. 0 to 250 Acceptable, 2. 250 to 500 Can be tolerated, 3. 500 to 1 000
Undesirable, 4. Over 1 000 Unsatisfactory.Experiment
Weigh a clean dry evaporating dish.
Put the filtered rain water in the evaporating dish and heat to dryness.
If heated too rapidly, the solution "spits" and some solids may be lost.
When you evaporate the solution to dryness, cool the evaporating dish
and leave it in a desiccator for one day.
Record the weight of the dissolved solids.18.2.3 Tests for soluble solids
in rain water
See: Water water quality, colorimeter, (Commercial)
Observe the dried filtrate under a microscope to identify its origin,
e.g. sand, soot, organic matter or coal washing residues.18.2.4 Tests for contamination
of groundwater from refuse deposits
The main problem of waste disposal today is the possible contamination
of groundwater by direct seepage from refuse deposits or by
substances leached from such deposits.Experiments
1. Support a funnel with a top diameter of 100 mm with a support stand
using a right angle clamp and a universal clamp.
Put a small wad of cotton wool in the funnel and then fill it with soil
to within a thumb width of the top.
Put a beaker beneath it.
Spread about 1 g of copper (II) sulfate on the soil and pour water over
it.
The water dissolves the copper (II) sulfate and seeps into the soil.
After a few minutes the blue copper (II) sulfate solution drips from the
funnel into the beaker placed beneath it.2. Spread an equal amount of sodium sulfate, potassium
sulfate or ammonium sulfate on the soil in the funnel, instead of copper
(II)
sulfate.
The liquid dripping into the beaker from the funnel will be colourless
or slightly yellowish from the soil.
Acidify it with hydrochloric acid and add 2% barium chloride solution.
A thick white precipitate of barium sulfate forms (sulfate test).3. Hazardous wastes must be disposed on in a geologically
responsible way, usually by incineration in special furnaces.
Hazardous wastes include pesticides, car batteries, petrol, oil, swimming
pool chemicals, solvents, aerosol products, fire extinguishers,
barbecue gas bottles, paint fluorescent lamps and tubes.
Ask your local city council or town council how hazardous wastes should
be disposed of and what facilities for disposal are available
to individual householders.18.2.5 Salinity
See: Salinity, (Commercial)
See: Water Water quality, (Commercial)
The salinity is the total solids, "salts", in water after all carbonates
have been converted to oxides, all bromide and iodide have been
replaced by chloride, and all organic matter has been oxidized.
So it is a measure of the total dissolved salts in a water sample, mainly
Ca, Mg, Na, bicarbonate, Cl and sulfate.18.2.6 Conductivity, TDS and
electrical conductivity
See: Meters environment meters, conductivity, TDS, (Commercial)See diagram 18.2.6: EC and TDSSee 6.3.1.3: Distilled water
1. Electrical conductivity (EC) measures the capacity of water to conduct
electrical current, so is directly related to the concentration
of salts dissolved in water, Total Dissolved Solids (TDS).
Salts dissolve into positively charged ions and negatively charged ions,
which conduct electricity.
Portable meters are used in the field to measure electrical conductivity
where it is difficult to measure TDS.
Distilled water does not contain dissolved salts to conduct electricity,
so has an electrical conductivity of zero.
However, at high salt concentrations electrical conductivity is not directly
related to salts concentration.
TDS (ppm) = 0.64 × EC (μS / cm) (microSiemens / cm).2. The total dissolved solids in water can be measured
by evaporating a water sample but it is more convenient to use methods
based
on water conductivity.
The conductivity is a measure of how well a water sample transmits an
electric current.
It depends on the ionized substances dissolved in the water and temperature.
Conductivity is expressed in umhos per cm, and is usually measured across
one centimetre.
Deionized water is a poor conductor of electricity with conductivity 0.5
to 2 umhos / cm.
However, water containing dissolved salts shows greater conductivity.
Usually conductivity is directly proportional to the concentration of
dissolved salts in the water.
The conductivity of potable waters may range from 50 to 1500 umhos / cm.
Dissolved ionic matter can be estimated from conductivity by multiplying
by 0.54 to 0.96, depending on components in water and
temperature.
Total dissolved solids, TDS, is the concentration of minerals and salts
impurities in the water, measured in parts per million, ppm.
(1 ppm = 1 mg per litre).
Specific conductivity is expressed as mhos per centimetre (M / cm) i.e.
siemens per centimetre, S / cm.
However, the mho (siemen) is a large unit, so usually the millimhos (millisiemen)
(mS / cm) is used.
A value of 0.67 is commonly used to convert conductivity as mS / cm into
total dissolved solids as ppm.
TDS ppm = Conductivity 0.67 S / cm × 0.67.
Electronic conductivity instruments can automatically compensate for temperature
and correct readings to 25oC.
Many authorities think that potable water should contain less than 500
ppm of dissolved solids.18.2.6.1 Tests for electrical
conductivity with a conductivity meter
See: pH (Commercial)
Remove the conductivity meter protective cap.
Stir the sample with the sensor tip for a few seconds, until the readings
stabilize.
Record value as micromhos per centimetre.
Estimate total dissolved solids by multiplying the conductivity by 0.67.
Rinse the sensor tip with deionized water.
(conductivity: mho (ohm backwards) = 1 siemens (s) = ohm -1 =
amps / volts).18.2.7 Cations and anions
in rain, rivers and sea water
Average chemical composition of natural waters, quoted by J. N. Butler,
Carbon Dioxide Equilibria and Their Application,
Addison-Wesley, Reading, MA, 1982, Chapter 5
Table 18.2.7 Cations and anions in rain, rivers and sea water

Ion

Rain

Rivers

Sea water

Ca2+

.

0.53

10.6

Mg2+

.

0.21

54.6

Na+

0.009

0.39

479.0

K+

.

0.036

10.2

H+

0.072

.

.

NH4+

0.016

.

.

HCO3-

.

1.1

2.3

SO42-

0.028

0.21

28.9

Cl-

0.012

0.23

546.0

Br-

.

.

0.85

F-

.

0.008

0.07

NO3-

0.026

0.017

0.0001

H2SiO42-

.

0.15

.

18.3.0a Tests for air and
dissolved oxygen in water
A good indicator of the health of water is how much air is dissolved.
Low air levels usually mean high levels of water pollution.
The mass of air that dissolves in water depends on the temperature of
the water.
When water is heated to near boiling point, the dissolved gases become
less soluble.18.3.1 Tests for air dissolved
in a water sample
Stand a beaker of water in sunlight.
Bubbles of air appear.
The taste of boiled water is different from tap water because boiled water
has lost its dissolved oxygen.
Note the temperature of a sample of water.
Boil the water until no more bubbles appear.
Collect the air from the water in an inverted measuring cylinder.18.3.2 Oxygen content of water,
dissolved oxygen, DO (Winkler method)
See: Salinity, (Commercial)18.3.3 Tests for dissolved oxygen, titration
1. The oxygen content of pure water is usually 7 to 10 mg per litre, depending
on the temperature and atmospheric pressure.
The following table shows the effect of temperature, at a constant pressure
of 1013 mb (millibar) 760 torr.
(1 mm mercury 133.3 Nm-2)
The solubility of dissolved oxygen decreases as salinity increases.
Table 18.3.2 Dissolved oxygen, DO

Temperature oC

Oxygen saturation mg / L

0

14.16

5

12.37

10

10.92

15

09.76

20

08.84

25

08.11

30

07.53

35

07.04

40

06.59

2. In natural stretches of water, the oxygen content
is also affected by oxygen consumption because of contamination and the
breakdown process associated with it, and the production of oxygen because
of the assimilation of underwater plants.
The oxygen wasting processes predominate, i.e. if the loading because
of insufficiently purified, effluent, for example, is too great, the
stretch of water will gradually become a stinking, repulsive sewer in
which life is no longer possible.3. A sufficiently accurate test for determining
the oxygen content of a water sample in schools is possible from the oxygen
determination method devised by L. W. Winkler.
This method uses the fact that when a manganous salt solution (e.g. manganous
sulfate) is treated with caustic soda, a white precipitate
of manganous hydroxide is produced.
MnSO4 + 2 NaOH ---> Mn(OH)2 + Na2SO4
In the presence of oxygen, the manganous hydroxide is oxidized to brown
hydrated manganese oxide.
2Mn(OH)2 + O2 ---> 2MnO(OH)2
The formation of hydrated manganese oxide is proportional to the amount
of oxygen, so the intensity of the brown colouration is an
indication of the oxygen content.
The precipitate produced by the addition of manganous sulfate solution
and caustic soda solution is coloured almost brown depending
on the oxygen content of the water sample.
The oxygen content may be estimated from the colouration.
If the precipitate remains white or almost white, there is no oxygen or
very little oxygen present.
If the precipitate is light yellow, the water sample contains little oxygen.
If the precipitate is coloured brown, it is rich in oxygen.18.3.3 Tests for dissolved
oxygen, titration
Manganese ions react with potassium iodide to produce iodine.
Titrate the iodine with sodium thiosulfate using starch as an indicator.
Lower a sampler into the water from a convenient place, e.g. a bridge.
Collect a water samples 1 metre below the surface by pulling a
string attached to the stopper of the sampler.
When bubbles no longer rise to the surface, note the water temperature
and pull up the sampler.
Check the sample for bubbles that can give a false, high reading.
To the sample add 8 drops of manganous sulfate solution and 8 parts of
alkaline potassium iodide azide.
A precipitate forms.
Add 8 parts of 1 to 1 sulfuric acid.
Shake the sample until the reagent and the precipitate dissolve.
The colour of the sample is now clear yellow if dissolved oxygen is low
to brown-orange if dissolved oxygen is high.
Add 8 parts of the starch indicator solution to the sample so that it
turns blue.
Titrate the sample against known molarity sodium thiosulfate solution
until the blue colour becomes colourless through the water sample.
Record the results as ppm dissolved oxygen.18.4.0 Tests for ions in a
water sample
Use the following test solutions:
Table 18.4.0 Test solutions

For Cl-

AgNO3 solution turns milky white

For SO42-

BaCl2 solution turns milky white

For Pb2+

Na2S solution forms a black precipitate

Evaporate a water sample in a non-aluminium container.
Heat slowly to avoid "spitting" when little water remains.
Dissolve the crystalline mass after evaporation in 10 mL of deionized
water.
Add one drop of test solution and record the results.18.4.1 Tests for phosphate
ions in water
Excess phosphate ions in water can cause eutrophication.
Most modern detergents do not contain phosphate ions.
To check this, do the following experiment with 1 g of detergent dissolved
in 1 g of water.
Dissolve 1.5 g di-sodium hydrogen phosphate (Na2HPO4.12H20)
in deionized water and make up to 1 litre.
Make solutions with nine different concentrations by making up to 100
mL with deionized water the following volumes and label the
containers with the concentrations.
Be careful! Use a burette or a pipette with rubber suction attachment.
Do not suck by mouth!
Add 15 g of ammonium molybdate (VI)-4-water ([NH4]2MoO4]
to 150 mL deionized water in a flask in crushed ice.
Leave the solution to cool.
Add 250 mL concentrated sulfuric acid to 250 mL deionized water.
Stop adding the acid when the flask becomes too hot, then leave it to
cool in ice.
Slowly add the cold ammonium molybdate solution to the cold sulfuric acid
solution.
Add 10 mL of ammonium molybdate and acid solution to each of the nine
phosphate solutions.
Add 10 mL of ammonium molybdate and acid
solution to a 100 mL sample of water.
Add crystals of L-ascorbic acid and boil.
Compare the colour with the colour of the standard solutions.
This technique is called colourimetric analysis.
Table 18.4.1 Phosphate ions in water

L phosphate (20 ug / L)

20 mL phosphate (4 ug / L)

75 mL phosphate (15 ug / L)

10 mL phosphate (2 ug / L)

50 mL phosphate (10 ug / L)

5 mL phosphate (1 ug / L)

40 mL phosphate (8 ug / L)

0 mL phosphate (0 ug / L)

30 mL phosphate (6 ug / L)

.

18.5.1 Tests for environment
of river, lake or ocean
1. Sample number, names of testers
2. Location: Distance from shore and location upstream or downstream from
a marker
3. Date and time
4. Weather: Fine or cloudy or rainy, wind speed and direction
5. Air temperature, daily range, oC
6. BOD, Biochemical Oxygen Demand, mg / L
7. Colour and appearance.
Compare the colour of the water against a white background.
Appearance: scum, muddy, clear, brown, foamy, milky.
8. Current flow and depth: stagnant, calm, brisk, raging.
9. Detergents: Half fill a flask with river water, insert a stopper and
shake for one minute, rate as "no detergent" if bubbles disappear
in less than three seconds, rate as "slightly frothy" if the bubbles take
up to ten seconds to break up, rate as "frothy" if the froth takes
up to five minutes to disperse.
10. Dissolved oxygen, ppm, % saturation
11. Faecal coliform bacteria colonies / 100 mL
12. Microscopic examination: Note the size of suspended particles and
any life forms, e.g. algae.
13. Oil or petrol: Look for the rainbow effect of petrol or oil on water.
14 pH
15. Smell: no distinctive character, musty, fresh, putrescence, earthy,
sewage-like, putrid, like liquid manure, peaty, chemical. 16.0 Turbidity
17. Total nitrates, mg / L
18. Total phosphorus, mg / L 19.0 Total solids
20. Visibility: Use a Secchi disc at depth of one metre
21. Water temperature, daily range, oC
Each item can be given a comparative rating so that an overall rating
can be calculated for comparison with other sites.16.0 Tests for turbidity
See: Water quality, Turbidity
sensor, Secchi Disk, (Commercial)
Turbidity, mg / L.
Observe settling on standing after 30 minutes.
Precipitate any fine suspensions and colloids that pass through the filter
paper by adding aluminium potassium sulfate (potassium alum,
Al2(SO4)3.K2(SO4).24H2O)
then filter.
However, you can also use device called a nephelometer to measure turbidity,
NTU.19.0 Total solids
See: Water quality, TDS,
Total dissolved solids, (Commercial)
Total solids, mg / L, Conductivity, umhos / cm, conductivity × 0.67 =
TDS, total dissolved solids, Floating debris.18.5.1a Eutrophication of
waterways
Waterways can be have excess plant nutrients from leaching of land, especially
agricultural land containing excess fertilizers, and
discharge of effluents containing nitrogen and phosphorus.
Decay of water weeds and other primary organic matter causes depletion
of oxygen especially in the summer, e.g. decay of
Eichhornia crassipes, water hyacinth, "the worst weed in the world",
South America, Pontederiaceae.18.5.2 Tests for anions in
sewage and tap waterSee 12.11.5.0: Tests for anions
in unknown solution, tests for acid radicals in solution
Compare concentrations by comparing the intensity of colour or amount
of precipitate.18.5.3 Tests for water samples
See: Water sampling, (Commercial)
See: Salinity, (Commercial)
See: Spectrophotometers, (Commercial)
See: Spectrophotometer (Commercial)
A list of tests used by some senior chemistry classes
1. Salinity: meter and refractometer
2. Turbidity: Tube and meter
3. Nitrite: Hach test strips
4. Nitrate: Hach test strips and spectrophotometer (OxidN in guidelines)
5. Phosphate: Hach test strips and spectrophotometer (convert to FiltRP
in guidelines)
6. pH: Narrow range Neutralist pH strips and meter
7. Dissolved oxygen: Meter and spectrophotometer
8. Conductivity: Meter. Many individual tests are necessary to detect
with certainty the purity or contamination of a stretch of water, including
physico-chemical, bacteriological and biological test methods.
You can study water samples taken from a river before and after passing
through a community area.
The physico-chemical examination of the water samples can include tests
for the presence of pollutant indicators besides determining
the smell, colour, temperature, and oxygen content.
These pollution indicators are substances because of contamination with
faecal matter in the water.
However, many of these compounds are normally present in water in small
amounts so precise guidelines and maximum permitted
values have been decided.
Occasionally, however, these values may differ considerably from the specified
figure, because of geological conditions for example,
although no contamination of a type that is harmful to health may be present
in the water.
The results of the individual physico-chemical tests must therefore only
be used as a whole for assessing the quality of water.
A selection of the most important physico-chemical tests for judging the
purity or contamination of a stretch of water, which can also
be done without great expense using facilities available in schools is
given below.18.6.0.1 Commonly occurring
air pollutants, safe air and clean air
In new estimates released on 25 March, WHO reports that in 2012 around
7 million people died (1 in 8 of total global deaths), as a
result of air pollution exposure.
This finding more than doubles previous estimates and confirms that air
pollution is now the world's largest single environmental health
risk.
The new data reveal a stronger link between both indoor and outdoor air
pollution exposure and cardiovascular diseases, such as
strokes and ischaemic heart disease, as well as between air pollution
and cancer.
Much of the burden results from burning of fossil fuels, and the new figures
underline the opportunity for more sustainable development
choices to simultaneously save lives and mitigate climate change.
Table 18.6.0.1 Air pollutants

Pollutant

Source

Health

Safe air

Clean air

sulfur
dioxide

sulfur in fuel

lung disease

2 pphm
(annual mean)

0.01
ppm

nitrogen
oxides

high temperature
combustion

lung disease

16 pphm2(1 hour average)

< 0.01
ppm

dust,
soot

combustion, mining,
land clearing

lung disease
if acid gases

90 mg / m3 TSP,
(annual mean)

10-20
g / m3

ozone

nitrogen oxides
and carbon

lung irritation

12 pphm
(1 hour average)

nil

lead

smelting,
leaded petrol

cumulative
poison

1.5 mg / m3
(3 month mean)

nil

carbon
monoxide

motor vehicle
combustion

body motor
functions

9 ppm2
(8 hour average)

< 1
ppm

mg = micrograms, pphm = parts per hundred million, ppm = parts per million,
TSP = total suspendable particulate18.6.0.2 Indoor air pollution,
formaldehyde pollution
The pollution in an indoor environment includes: suspended particulates,
smoke nuisance, volatile and semi-volatile organic
compounds, formaldehyde, and burning gases.
Formaldehyde pollution is caused by 1. pressed wood products (hardwood
plywood wall panelling, particle board, fibre board) and
furniture made with these pressed wood products, 2. urea-formaldehyde
foam insulation (UFFI), 3. combustion sources and
environmental tobacco smoke, 4. durable press drapes and other textiles,
5. glues.
Formaldehyde gas can cause watery eyes, burning sensations in the eyes
and throat, nausea, and difficulty in breathing in some humans
exposed at elevated levels (above 0.1 parts per million).
Health effects include eye, nose, and throat irritation; wheezing and
coughing; fatigue; skin rash; severe allergic reactions.
Average concentrations in older homes are usually well below 0.1 ppm.
In homes with many new pressed wood products, levels can be greater than
0.3 ppm.18.6.2 Tests for air pollution
from burning refuse
Considerable pollution of the environment by harmful combustion products
can be caused by the burning of rubbish that is often done
without proper understanding.
A typical example is the burning of polyvinyl chloride (PVC).
This synthetic plastic is used to make many types of domestic objects and
packaging material later scrapped to become refuse.
When burnt, chlorine in its molecules is converted to hydrogen chloride
dissolving in water to form dilute hydrochloric acid.
The World Health Organization advises that the acceptable level of fine
particles in the air measuring less than 2.5 microns, known as
PM2.5, should be no more than 25 micrograms per cubic metre.
Above 300, and the United States Environmental Protection Agency warns
outdoor activity becomes hazardous, even for healthy adults.
On January 12, 2013 in Beijing, the PM2.5 pollution hit 886, officially
off the charts for dangerous air quality.
The problem is not limited to Beijing because many other cities in China
have also been suffering from air pollution.Experiments18.6.2.1 Tests for air pollution from burning refuse
1. Metaldehyde
A few small PVC rods are laid on two small tablets of solid fuel (Esbit,
Blitzem, firelighter, "meta" fuel, canned heat, snail bait,
metaldehyde, in a porcelain basin.
A strip of moistened, blue litmus paper is hung 25 cm above the basin,
using a support rod, a right angle clamp and a universal clamp.
The fuel is set alight and the PVC is burnt.
Within no more than a minute, the blue litmus paper is turned red by the
hydrochloric acid formed by the burning PVC.
The experiment should be done in a fume cupboard.
Prove that the red colouration of the blue litmus paper is because of combustion
of the PVC, two tablets of solid fuel without any PVC
are burnt in a parallel experiment.
The colour of the blue litmus paper is unchanged even after the two tablets
have completely burnt away.2. Put a porcelain dish containing a tablet of
solid fuel and PVC rods on a glass plate.
The solid fuel tablet is easier to ignite when it is broken in two and
one piece is placed at an angle across the other.
Use a 5 litre glass bell jar with a strip of moistened blue litmus paper
secured by a rubber stopper hanging 10 cm inside the neck.
Invert the glass bell jar over the porcelain dish when the solid fuel
has been ignited.
Although only a little PVC burns in the small amount of air enclosed
under the bell jar, the litmus paper colour turns strongly to red.
These experiments show that rubbish should be deposited only on sites
where the nature of the ground makes it unlikely that
groundwater can become polluted by substances leached from the rubbish.
Burning of the rubbish to reduce its bulk should be permitted only in
appropriately designed refuse destructors in which the resulting
combustion products can be rendered harmless.18.6.3 Danger of vehicle exhausts,
tailpipe gases
Exhaust gases from motor vehicles contain lead dust (5 to 30 mg / m3),
nitric oxide (0.005 to 0.3% by volume), hydrocarbons
(0.01-1%), and carbon monoxide (1-10% by volume).
Carbon monoxide is very dangerous to humans, because it cannot be detected
by the senses because it has no colour, smell or taste.
Its affinity to haemoglobin is 250 times that of oxygen.
During carbon monoxide poisoning, a rapid breakdown in the supply of oxygen
to the body occurs, leading to headaches and
dizziness at low concentrations.
At high concentrations (0.2% by volume) it can very rapidly lead to death.
To monitor the carbon monoxide content of the air you can use a carbon
monoxide gas detector, e.g. the gas detector, that
allows detection of concentrations as low as 0.001% by volume.Experiments18.6.3.1 Tests for carbon monoxide with a gas detector
Make ten strokes of the pump and squeeze the bellows of the pump until
their limit, so the suction stroke admits100 mL of air.
The colour of the preparation in the test-tube changes while the pumping
is in progress.
The white indicator layer, which contains iodine pentoxide (I2O5)
as the effective reagent with fuming sulfuric acid (H2S2O7)
turns
brown-green during the reaction time, under the influence of selenium
dioxide (SeO2) as catalyst.
The reaction can be described by the following equation:
SeO2 + H2S2O7
5CO + I2O5 ---> I2 + 5CO2
The length of the coloured zone depends on the carbon monoxide concentration.
The carbon monoxide content of the air, in percentage volume can be read
directly on the printed scale.
MWC, maximum working concentration, is that concentration in the air of
a workshop, measured in depth of breathing, at which no
damage to health is to be expected, even with exposure during the day.
Comparative measurements of the carbon monoxide content of the air should
be repeated under different weather conditions,
because the carbon monoxide content of the air depends on rain, mist,
wind, sunshine and smog conditions with an inversion layer.
Table 18.6.3 Carbon monoxide effects

CO content of the
air in vol.
per cent

CO concentration
in ppm

CO concentration
in the blood

Effect on humans

0.01

100 (MWC)

10 to 20%

no perceptible effect

0.025

250

30%

headaches, slight fatigue

0.05

500

40 to 50%

headaches, collapse and
fainting on exertion

0.1

1000

60 to 70%

unconsciousness,
cessation of breathing
on prolonged action

0.2

2000

>70%

instant death

Nowadays, direct plug-in electrochemical 12-24V in-car carbon monoxide
alarms are available to help detect dangerous levels of
carbon monoxide in motor vehicles and workshops.18.6.4 Water tests
Use individual tests to find the degree of purity or contamination of
water.
Tests include physicochemical, bacteriological and biological tests.
Do the tests at sites in a river before and after passing through a community
area.
Test for the presence of "pollutant indicators" besides determining the
smell, colour, temperature, oxygen content.
These indicators are substances in the water because of contamination
with faecal matter.
Many of these compounds are normally present in water in small amounts
so precise guidelines and maximum permitted values must be
laid down.
These values may differ considerably from the specified figure, because
of geological conditions, although no contamination of a type
that is harmful to health may be present in the water.
So the results of the individual physico-chemical tests must be considered
as a whole for assessing the quality of water.
Some more important physico-chemical tests for judging the degree of purity
or contamination of water are described below.18.6.5 Smell of water, hydrogen
sulfide
1. Water used for drinking must not smell unusual, repugnant, or revolting.
Many substances can affect the smell of water.
The bad smell of underground water may be caused by hydrogen sulfide that
can be produced by the reduction of iron sulfide.
Make a preliminary test of smell to provide initial information when the
sample is taken because some smells, like that of hydrogen
sulfide, may rapidly disappear.
You can more readily detect odours if the substance is heated slightly.
Hydrogen sulfide, when dissolved in water, produces an offensive odour
resembling that of rotten eggs.
The presence of hydrogen sulfide in deep well water is because of the
reduction of sulfate.
The acceptable level of hydrogen sulfide is 0.05 mg / L or less.
Hydrogen sulfide can be removed through oxidation or by aeration or chlorination.2. The precipitated sulfur should be removed by
filtration to prevent it from reverting back to hydrogen sulfide through
the action of
certain micro-organisms.
The oxidation of hydrogen sulfide by chlorine may be advantageous in cases
where it is otherwise unnecessary to repump the water,
normally required with aeration, because chlorine can be applied directly
into the system.
Enough chlorine must be used to maintain a distinct chlorine residual.Experiment18.6.5.1 Tests for smell of water
Put 100 mL of the water sample in a 250 mL wide mouth bottle.
Close with a glass stopper and heat in a water bath to 40oC.
After shaking it vigorously, open the bottle and test the smell of the
water immediately.
Unbiased measurement of smell by means of numerical values is impossible
but use the following terms to describe the smell:
1. no distinctive character, 2. musty, 3. fresh, 4. putrescence, 5. earthy,
6. sewage-like, 7. putrid, 8. like liquid manure, 9. peaty,
10. chemical.
The general description "chemical" can be amplified, as smelling of hydrogen
sulfide, chlorophenol (pharmacy shop smell), chlorine, tar,
ammonia, mineral oil, phenol.
Use the terms "slight or "pronounced" to describe the intensity of the
smell.18.6.6 Colour of water
1. Pure, clean water is colourless or possibly just slightly bluish in
colour.
A colour other than this may be because of the most different kinds of
foreign or contaminating matter.
Thus humus materials generally produce a yellow brown colouration, iron
a yellowish reddish one, micro-organisms, e.g. plankton
organisms may give a greenish, yellowish or brownish colour to the water.
Water that is distinctly contaminated has a greyish yellowish to grey
black colour.
Different substances that may cause differing amounts of harm may produce
similar discolouration so an unbiased measurement using
numerical values is impossible.
It follows that the colour of water used for assessing its quality must
be used only with all the other test results.
Devices called tintometers can be used to record water colour.
The name of a colour may be based on the "Munsell colour chart".Experiment18.6.6.1 Tests for colour of water
2. Use two tall colourless glass beakers.
Put 200 mL of the water sample in one beaker.
Put the same amount of deionized water in the other beaker.
Put both beakers on a white background, e.g. a sheet of writing paper or
a white tile.
Compare the colour of the water sample, as viewed from above, with the
colour of the distilled water.
Colour can be described as: colourless brown, slightly yellowish, yellowish
green, yellowish, greenish, yellow, green,
yellow brown, grey yellow, brownish, grey black.
The room must be well-lighted by daylight.18.6.7 Hydrogen ion concentration
of water
See: pH (Commercial)
1. Pure water is very slightly dissociated, i.e. split into its ions (H+
and OH-).
One litre of pure water contains 1 / 10 000 000 (10-7) g of
hydrogen ions (H+).
Since the same amount of hydroxyl ions (OH-) is also present,
pure water has a neutral reaction.
Instead of the value 10-7, the pH value is used, which is the
logarithm of the reciprocal of the hydrogen ion concentration.
Water with a pH value of 7 is neutral; below it is acid and above 7 it
is alkaline.
Natural stretches of water usually have a pH value approximating to that
of the neutral point.
Extreme values occur, because soil from which the water originates, are
pH 3 in the acid range and pH 12 in the alkaline range.
The organisms living in water thrive best of all at a pH between 6.8 and
7.8.
Changes of hydrogen ion concentration, e.g. because of the introduction
of insufficiently neutralized industrial effluent, may cause gross
disturbances in the ecological equilibrium.
Also, the changes may cause the direct poisoning of underwater life because
of the materials introduced.Experiment18.6.7.1 Tests for hydrogen ion concentration of
water
The simplest way to find the pH value is to use universal indicator paper,
pH 1 to 10, for the whole pH range and as special
indicator paper for various pH ranges, e.g. indicator rods: pH 2.5 to
4.5, pH 4.0-7.0, pH 6.5 to 10.0.
First wet a strip of universal indicator paper the water sample.
After one minute find the pH value by comparing the colour produced with
that of the colour scale provided.
The colour scale of the universal indicator paper is subdivided into complete
pH units.
By estimating the intermediate stages, half pH units can also be read
off.
The test is repeated in the same way, using a strip of special indicator
paper of the corresponding pH range.
The graduation of the colour scale of the special indicator paper is so
fine that 2 / 10 of a pH unit can be read off.
By this means, you can find the hydrogen ion concentration of a water sample
with an accuracy sufficient for school purposes.
For more accurate measurements use a battery-operated electronic pH meter.18.6.8 Temperature of water
1. Drinking water should be neither too hot nor too cold and have a temperature
between 8oC and 12oC.
Colder water is generally regarded as unacceptable.
At temperatures below 5oC, stomach or intestinal troubles may
even occur.
Water at a temperature of more than 15oC has no longer a refreshing
effect.
The temperature is important for the ecological equilibrium of water, because
the oxygen content of water is very closely related to it.
The introduction of large amounts of insufficiently-cooled cooling water
into a river by an industrial undertaking may have severe
consequences and contribute to the mass death of fish Experiment18.6.8.1 Tests for temperature of water
Tie a rope, e.g. a Perlon cord 0.5 mm in diameter, just above the spherical
bulb at the lower end of an aquarium thermometer.
Also, a piece of metal, e.g. an old key, is attached to make it sink in
water.
Tie pieces of red string at intervals of 25 m.
This device allows temperatures to be taken at various depths in water.
The thermometer is let down, the depth of water is recorded, and after
two minutes it is pulled up quickly and the temperature
immediately read.
Temperature measurements on water samples are done in the workroom using
a chemical thermometer.18.6.9 Colorimeter tests, test methods
See: Colorimeters, (Commercial)
Aluminium to Eriochrome, Cyanine R
Ammonia to Nitrogen, Salicylate
Ammonia to Nitrogen, Nesslerization,
Bromine to DPD, Tablets
Chlorine to DPI, Tablets
Iodine to DPI, Tablets
Chlorine Dioxide to DPI, Tablet / Glycine
Chromium (Hexavalent) to Diphenylcarbazide
Chromium (Total, Hexa and Trivalent) to Diphenylcarbazide
COD, Low to Digestion (mercury free)
COD, Low to Digestion contains mercury
COD, Standard to Digestion (mercury free)
COD, Standard to Digestion (contains mercury)
COD, High to Digestion (contains mercury)
Copper to Diethyldithiocarbamate
Copper to Bicinchoninic Acid
Cyanide to Pyridine to Barbituric Acid
Cyanuric Acid to Melamine
Fluoride to SPADNS
Hydrazine to P to dimethylaminobenzaldehyde
Hydrogen Peroxide to DPI Tablets
Iron to Bipyridyl
Iron to 1, 10 Phenanthroline
Manganese (LR) to PAN
Manganese (HR) to Periodate
Molybdenum to Thioglycolate
Nickel to Dimethy1glyoxime
Nitrate Nitrogen to Cadmium Reduction
Nitrite Nitrogen to Diazotization / Coupling
Oxygen, Dissolved to Winkler colourimetric
Ozone to Indigo Trisulfonate
pH (5.0 to 9.6) to colourimetric
Phenols 4 to Aminoantipyrine
Phosphate (HR) to Molybdovanadate
Phosphate (LR) to Ascorbic Acid Reduction
Potassium to Tetraphenylboron
Silica (LR) to Heteropoly Blue
Silica (HR) to Silicomolybdate
Sulfate to Barium Chloride
Sulfide to Methylene Blue
Tannin to Tungsto to Molybdophosphoric Acid
Turbidity (0 to 400 FTU) to Absorptimetric
Zinc to Zincon.18.7.1 Drinking water test
media
Bismuth Sulfide Agar, Brilliant Green Agar, Brilliant Green Bile Lactose
Broth, Cetrimide Agar, DCLS Agar, ENDO Agar (Base),
Formate Ricinoleate Broth, MacConkey Agar No 1, Malachite Green Broth,
Methyl Red Voges Proskauer Broth, Nutrient Broth No 3,
Peptone Water, Phenylalanine Agar, Plate Count Agar, Selenite Broth (Base),
Simmons Citrate Agar, SS-Agar, Tetrathionate Broth,
TetrathionateBroth (Base), Triple Sugar Iron Agar, Tryptic Soy Broth, Tryptone
Glucose Extract Agar, Tryptone water, Urea Broth,
Violet Red Bile Agar.18.7.2 Effect of household
detergents on freshwater organisms
Most detergents are "biodegradable", but degradation takes time, so detergents
in rivers may be harmful before being degraded.
Detergents may affect the permeability of biological membranes.
Investigate the tolerance of certain freshwater organisms to different
concentrations of detergents.
Use different organisms for testing, e.g. Daphnia, freshwater snails,
small fish, the monocotyledon duckweed Lemna, and tadpoles.18.7.0 Bottled water
For many years, we relied exclusively on rain water or tap water for drinking.
Now that consumers are turning to bottled water as the healthy and "pure"
alternative to tap water, are we really just wasting our
money and the environment? Spring water is extracted from natural sources.
Other bottled water is simply water from the municipal water supply that
has been subjected to additional treatment.
Consumers may claim that bottled water is convenient and that it tastes
better than tap water.
It is also marketed as the healthy alternative to sugared drinks and as
the most "pure" available water.
But the health arguments for bottled water are overstated.
The choice is not one between sugared drinks and bottled water, but between
bottled water and tap water.
There is no evidence that bottled water is more "pure" than tap water,
but plenty of evidence to suggest that bottled water is costly:
both to the hip pocket and to the environment.
During extraction spring water is extracted from underground aquifers
upstream from where the water surfaces.
This disrupts aquifer flow, affecting flora and fauna.
In production, most bottled water is packaged in PET (polyethylene terephthalate)
plastic bottles, which are derived from crude oil.
It can take up to 3L of water to produce 1L of water.
Transportation of bottled water around the world requires burning of fossil
fuels.
In landfill and the litter stream, although plastic bottles are recyclable,
many end up in landfill and take up to 1000 years to break down.
When littered they often end up in the sea where they break up in small
pieces, killing marine life that mistake them for food.
The best thing to do is to avoid bottled water.
Australian tap water is world standard drinking water so it is the safe,
cheap and sustainable option.
Install a tap filter if you are concerned about the taste or quality of
your local tap water.
Buy a reusable bottle.
There is a great range available from camping stores and other retailers.Using rivers for water testing
There are two experiment methods:
1. Manipulate one variable to see the effect on the other, keeping other
variables constant, e.g. What is the effect of temperature
(the manipulated or independent variable) on the concentration of Vitamin
C in orange juice (the dependent variable)?
2. Concomitant variation.
A naturally occurring variation (Variable 1) is correlated against another
variation (Variable 2).
The correlation method.
For example: How does temperature in the natural environment affect stoma
opening?
In this experiment you do not need you to control the environmental temperature,
but you do need to measure the dependent variable
at different temperatures.
However, there may be other potentially influential variables, e.g. humidity.
That does not preclude the variables in relationship being considered.
One way to address the other variables is to collect data on the other
variable as well and run the statistics on each pair of variables
separately.
Where the data are collected from a local river, the method used is the
second approach.
Students are relying on some naturally occurring change in water quality,
e.g. BOD, turbidity, temperature as one set of variables,
then trying to correlate this with the riverside development at sites
along the river.
However, there are so many confounding variables and the differences between
two sites may be many).
A river may be just used as a source of field data for collecting samples
for water quality testing.